1. Field of the Invention
The present invention is related to droplet ejecting apparatuses which conduct recording by ejecting droplets from droplet ejecting units to recording media, methods for cleaning droplet ejecting faces, and methods for cleaning wiping members mounted on droplet ejecting apparatuses.
2. Description of the Related Art
Droplet ejecting apparatuses which eject liquid ink from ejection openings, in particular inkjet recording apparatuses, have been uses as engines for many image forming systems recently because they are compact and inexpensive. Recording heads using piezoelectric systems (piezo-inkjet systems) are often used in inkjet printers because of their capability of forming high-definition image with high printing speed. In the piezoelectric systems, ink is ejected by driving piezoelectric elements through deformation thereof.
The PWA (Partial Width Array) system and FWA (Full Width Array) system are examples of the printing method (scanning method). In the PWA system, the recording head is moved in the direction (main scanning direction) which is orthogonal to the moving direction of the recording sheet while the recording sheet is moved at a predetermined pitch (sub scanning). In the FWA system, the recording head (full-line head) has a width which covers the entire width of the recording sheet (in the main scanning direction) and is fixed, and the recording sheet is moved in the sub scanning direction. In particular, the FWA system realizes a higher printing speed than the PWA system.
Inks containing pigments as colorants have conventionally been used for inkjet recording apparatuses having inkjet recording heads which conduct recording on recording sheets (recording media) by the ejection of ink droplets from nozzles. The use of pigments aims at the improvement of water resistance, light fastness, and the like. However, pigments themselves do not strongly adhere to the recording sheets. In order to improve the fixability on the recording sheets, inks further containing resins have been proposed.
However, ink leaks from the nozzles and also bounces back from the recording sheet during printing. As a result, ink adheres to near the nozzles and the resin as a solid component deposits thereon by drying. The deposition of the resin makes the ink meniscus instable, thus degrading the directivity of the ink droplets.
Towards the problem, a method has been proposed (for example in Japanese Patent Application Laid-Open (JP-A) No. 8-58096, the disclosure of which is incorporated herein by reference) in which a water-shedding film or a hydrophilic film is formed on the droplet ejecting face provided with the nozzles. However, even when this method is used, resin deposition occurs near the nozzles, the ejection of ink is impaired, and the directivity of the ink ejection is deteriorated during long-term use.
In order to make the nozzles on the droplet ejecting face conduct self-cleaning, there have been suggestions to provide a hydrophilic layer made of titanium oxide on the nozzle sheet (top plate), thereby decomposing ink dirt through photocatalytic reaction (see, for example, JP-A No. 2004-114619, the disclosure of which is incorporated herein by reference). However, when hydrophilicity is imparted to near the nozzles such as the nozzle sheet, ink leaks more easily to destabilize the formation of ink meniscus which largely affects the ejection of ink droplets. Particularly when the head structure adopts droplet modulation using the control of ink meniscus by a piezoelectric element or the like, the stability of the ejection is adversely affected.
Further, when the droplet ejection quantity is large, such as in the case of a printer equipped with the full-line head having plural ejection openings along the entire width of the recording region or in the case of high-speed printing in large quantity, the effect brought about by the technique is insufficient. Therefore, the problems concerning ink dirt have not been solved.
There are inks for inkjet recording which contain pigments. Inks containing pigments are advantageous in their high water resistance and light fastness and in capability of forming an image with high optical density. However, the inks are disadvantageous in the fixability of the image and the resistance to rubbing. In order to solve the problems, inks further containing resins are used.
When such an ink are used, the ink leaks from the nozzles and also bounces back from the recording sheet during printing to adhere to near the nozzles. As a result, the resin contained in the ink dries to deposit on near the nozzles. The deposition of the ink destabilize ink meniscus and deteriorates the directivity of the ejection of ink droplets.
A method for removing the dirt (such as dried resin) adhered to near the nozzles has been used in which the nozzle surface is cleaned by periodical wiping with a blade such as elastomer (see, for example, JP-A No. 57-34969, the disclosure of which is incorporated herein by reference). However, when this method is used, the resin deposits also on the blade during long-term use. As a result, the cleaning performance of the blade is deteriorated, so that the blade is no longer able to completely remove the resin or the like deposited on near the nozzles. Therefore, the directivity of the ejection of ink droplets is deteriorated.
Toward this problem, a method has been proposed, for example in JP-A No. 2000-000974, the disclosure of which is incorporated herein by reference. In this method, the dirt adhered to the blade is taken up by a suction device to clean the blade. However, sucked dirt accumulates in the sucking device in long-term use, whereby the suction efficiency of the suction device is lowered. Therefore, the dirt adhered to the blade cannot be completely removed by this method, either.